I'll post it in context. Psalm 19:7-9;
7The law of the Lord is perfect,
reviving the soul;
the testimony of the Lord is sure,
making wise the simple;
8the precepts of the Lord are right,
rejoicing the heart;
the commandment of the Lord is pure,
enlightening the eyes;
9the fear of the Lord is clean,
the rules of the Lord are true,
and righteous altogether.
"The fear of the Lord is clean." The doctrine of truth is here described by its spiritual effect, viz., inward piety, or the fear of the Lord; this is clean in itself, and cleanses out the love of sin, sanctifying the heart in which it reigns. Mr. Godly-fear is never satisfied till every street, lane, and alley, yea, and every house and every corner of the town of Mansoul is clean rid of the Diablolonians who lurk therein. "Enduring for ever." Filth brings decay, but cleanness is the great foe of corruption. The grace of God in the heart being a pure principle, is also an abiding and incorruptible principle, which may be crushed for a time, but cannot be utterly destroyed."